The complete email delivery platform
Email infrastructure your customers actually receive.
Send transactional and marketing email at scale with a SendGrid-compatible API, drag-and-drop campaign builder, 7-check email validation, per-domain DKIM authentication, and an enterprise-grade deliverability operations center your whole team can use. Trusted by developers, growth teams, and operators who refuse to compromise on inbox placement.
curl -X POST https://api.inbox.onesourcesoft.com/api/v1/mail/send \
-H "Authorization: Bearer $INBOX_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"personalizations": [{"to": [{"email": "ada@example.com"}]}],
"from": {"email": "hello@yourapp.com", "name": "YourApp"},
"subject": "Welcome to YourApp",
"content": [{"type": "text/html", "value": "<h1>Hi Ada</h1>"}],
"tracking_settings": {"open_tracking": {"enable": true}}
}'Live delivery feed
Streaming- ada@stripe-cust.comorder.shippeddelivered0.42s
- leo@acmecorp.ionewsletter.mayopened12s
- sara@bigco.netproduct.launchclicked38s
- ben@startup.devpassword.resetdelivered1.1s
- mia@example.cominvoice.sentdelivered0.6s
Trusted by teams shipping email at every scale
Built for businesses that take email seriously
Why teams choose Inbox OSS over SendGrid, Mailgun, and Postmark
A complete platform — transactional API, marketing campaigns, deliverability operations, and email validation — at honest, volume-based pricing with no per-feature upsell.
One platform. Every email your business sends.
Receipts, password resets, security alerts, abandoned-cart flows, weekly newsletters, product launches, system notifications, and re-engagement drips — all from a single account with consolidated reputation, unified analytics, and one API key. Most platforms force you to choose between transactional-only services and marketing-only services. Inbox OSS gives you both, with category-aware segmentation that keeps the right reputation on the right traffic.
Inbox placement as a discipline, not a setting.
Every signal mailbox providers use to score your reputation — complaint rate, bounce rate, blocklist appearances, postmaster scores, FBL reports, engagement decay — is instrumented and surfaced in plain language before placement degrades. Per-IP warmup is automated. DKIM, SPF, and DMARC alignment are enforced at send time. Our seven-check validation engine catches the spam traps and disposable domains that destroy reputation overnight.
Enterprise-grade trust, transparent pricing.
SOC 2 Type II audited annually. GDPR-compliant processing with a pre-signed DPA. HIPAA Business Associate Agreement available on Enterprise. AES-256 encryption at rest, TLS 1.3 in transit, Ed25519-signed webhooks. SSO via SAML and OIDC, SCIM provisioning, IP allowlists on every API key. All at volume-based pricing with no surprise overages and no per-feature upsell — every plan includes the full feature set.
One platform · every email
The complete email infrastructure stack
A unified system for transactional delivery, marketing campaigns, deliverability operations, list hygiene, and observability — under one API key, one bill, one consolidated reputation.
Transactional Email API
SendGrid v3-compatible REST API with eight first-class SDKs, idempotency keys, sandbox mode, and sub-100ms acceptance latency from six global regions.
Learn moreSMTP Relay
Drop-in SMTP for WordPress, Rails ActionMailer, Django, Laravel, and any legacy mailer. Username and API-key authentication, TLS 1.3 required, full deliverability tooling.
Learn moreMarketing Campaigns
Drag-and-drop builder, real audience segmentation, A/B testing on subject and content, send-time optimization, and category-aware unsubscribe groups.
Learn moreMarketing Automations
Visual flow builder for drip sequences, lifecycle campaigns, and behavior-triggered emails. Triggers on signup, tag change, custom event, or schedule.
Learn moreDeliverability Operations
Per-IP warmup automation, Spamhaus and Barracuda blocklist monitoring, feedback-loop ingestion, postmaster-tools integration, inbox-placement testing.
Learn more7-Check Email Validation
Syntax, DNS, SMTP probe, catch-all detection, risk-database lookups, MX blacklist checks, and WHOIS domain-age verification — the industry's deepest engine.
Learn moreAnalytics & Reporting
17 dashboards covering opens, clicks, bounces, complaints, geographical breakdown, device split, mailbox-provider performance, and revenue attribution.
Learn moreReal-time Webhooks
29 distinct event types delivered with Ed25519 signatures, 24-hour retry-on-failure with exponential backoff, and full replay history from the dashboard.
Learn moreInbound Email Parse
Receive email as structured JSON via webhook. Attachments parsed and stored. DMARC, SPF, and DKIM authentication results included on every payload.
Learn moreBuilt for developers
Drop us in. Don't change your code.
Inbox OSS speaks the SendGrid v3 API verbatim and provides a Mailgun-compatible v3/messages endpoint. Migration is typically two changes: your hostname (api.sendgrid.com → api.inbox.onesourcesoft.com) and your API key. Every SDK, template, webhook handler, and personalization rule you already wrote keeps working unchanged.
- Eight official SDKs: Node.js, Python, Go, Ruby, PHP, Java, .NET, and Rust — all generated from the same OpenAPI 3.1 specification.
- Idempotency keys on every write operation, retry-safe API design, server-side request validation, and structured RFC 7807 problem-details errors.
- Per-key scopes (send, read, manage) with optional IP allowlists, mandatory TLS 1.3 on the SMTP endpoint, and Ed25519-signed webhook payloads.
- Sub-100ms p99 acceptance latency from six anycast edge regions, durable acceptance with two-zone fsync before 202 response, automatic multi-region failover.
- Sandbox mode validates every request shape, authentication, and template syntax without consuming a credit or actually delivering — perfect for CI pipelines.
- OpenAPI 3.1 spec, postman collection, comprehensive CLI for local development, and a self-host option so you are never locked into our managed cloud.
import { InboxOSS } from '@inbox-oss/sdk';
const client = new InboxOSS(process.env.INBOX_API_KEY);
await client.mail.send({
to: 'ada@example.com',
from: { email: 'hello@yourapp.com', name: 'YourApp' },
subject: 'Welcome to YourApp',
html: '<h1>Hi Ada</h1>',
tracking: { opens: true, clicks: true },
categories: ['onboarding', 'welcome'],
});Marketers welcome
A campaign workspace your growth team will actually use
Real segmentation, real reporting, real automation — not just an API. Designed for marketers who refuse to file a Jira ticket every time they need to send a newsletter.
Drag-and-drop campaign builder
Visual editor with brand-kit colors and fonts, undo history, mobile preview, library of starter blocks, and an HTML/MJML escape hatch when you need pixel-level control.
Learn moreSmart audience segmentation
Build segments from any combination of tags, custom fields, behavioral filters, and engagement recency. Saved segments stay live as subscriber data changes.
Learn moreSend-time optimization
Machine-learning identifies the moment each individual subscriber is most likely to engage. Or schedule by recipient local timezone. Or pick a fixed broadcast time.
Learn moreUnsubscribe groups
Multiple subscription categories per account. Subscribers self-manage which streams they want without scorched-earth global unsubscribes that kill your reputation.
Learn moreA/B/n testing
Test subject lines, content variants, send times, or any combination. Auto-promote winners on opens, clicks, or revenue. Sample-size calculator built in.
Learn moreMulti-language & localization
Per-recipient locale routing, automatic RTL handling, CJK font support, and translation-friendly template syntax. Send the right language to every subscriber automatically.
Learn moreDeliverability scorecard
Inbox placement
98.7%
Spam folder rate
1.1%
Bounce rate
0.4%
Complaint rate
0.02%
DKIM signed
100%
DMARC pass
99.8%
Live reputation check
No listings on Spamhaus Zen, Barracuda Reputation Block List, or SURBL. Gmail, Yahoo, and Microsoft postmaster scores healthy across all sending IPs.
Deliverability that compounds
Your sender reputation is our north star.
Deliverability is not a setting you flip. It is a discipline practiced continuously across dozens of signals: authentication alignment, complaint rate, bounce rate, blocklist appearances, engagement decay, content patterns, and volume consistency. We instrument every one of them and surface degradation in plain language — before mailbox providers route you to the spam folder.
- Per-IP warmup schedule with automatic daily-limit adjustment based on real mailbox-provider response, not arbitrary curves.
- Bounce classification across hard, soft, out-of-office, content-block, policy-block, and reputation-block — so you do not punish legitimate transients.
- Real-time blocklist monitoring against Spamhaus Zen, Barracuda Reputation, SURBL, and SORBS. Alerts fire on first listing.
- Feedback-loop ingestion from Gmail, Yahoo, AOL, Hotmail, Comcast, and every other major provider — complaints route back to the originating campaign automatically.
- Gmail Postmaster Tools, Yahoo Sender Hub, and Microsoft SNDS integration. Daily reputation tier streams into the dashboard and optionally into your engineering Slack.
- Seed-list inbox-placement testing across 30+ ISPs gives you a real placement percentage on each campaign before you commit to a full send.
98.7%
Inbox placement
30-day rolling, top mailbox providers
<100ms
API p99 latency
From six global edge regions
14B+
Emails delivered
Across all customers, lifetime
7-check
Validation engine
Industry-leading verification depth
Side-by-side
How Inbox OSS compares to other email platforms
Honest, factual comparisons. We name competitors directly because we have nothing to hide — and our customers deserve a clear picture.
| Capability | Inbox OSS | SendGrid | Mailgun | Postmark |
|---|---|---|---|---|
| Transactional API | ✓ Native | ✓ Native | ✓ Native | ✓ Native |
| SMTP relay | ✓ TLS 1.3 | ✓ | ✓ | ✓ |
| Marketing campaigns | ✓ Included | Add-on tier | Limited | ✗ |
| Marketing automations | ✓ Visual builder | Pro tier | Limited | ✗ |
| Email validation (7 checks) | ✓ Built-in | Basic (3 checks) | Basic (3 checks) | ✗ |
| Per-IP warmup automation | ✓ Adaptive | Manual schedule | Manual schedule | Manual |
| Dedicated CSM | Pro & Enterprise | Enterprise only | Enterprise only | Enterprise |
| Open source / self-host | ✓ Available | ✗ | ✗ | ✗ |
| Free tier emails/month | 3,000 | 100/day (limited) | 100/day (limited) | 100 (trial) |
| Transparent pricing | ✓ Volume-based | Multi-tier upsell | Multi-tier upsell | Per-message |
| SOC 2 Type II | ✓ | ✓ | ✓ | ✓ |
| GDPR DPA + EU region | ✓ | ✓ | ✓ | ✓ |
| HIPAA BAA | ✓ Enterprise | Enterprise | ✗ | ✗ |
| SDKs (official) | 8 languages | 7 languages | 6 languages | 8 languages |
| Webhook signature scheme | Ed25519 | HMAC-SHA256 | HMAC-SHA256 | Bearer header |
Comparison data sourced from public pricing pages and feature documentation as of May 2026. We strive to keep this accurate — if you find an error, email hello@inbox.onesourcesoft.com and we will correct it within 24 hours.
Trusted by builders
Real teams. Real numbers. Real inboxes.
The teams that switched tell us the same thing: better deliverability, fewer surprises, real humans in support.
“We migrated from SendGrid in a single afternoon. Our spam-folder rate dropped from 3.4% to 0.8% in the first week. The deliverability audit they ran during onboarding caught three misconfigured templates that had been quietly hurting us for 18 months.”
Mira Patel
Staff Engineer · Loop
“The validation engine paid for itself in three days. Our bounce rate dropped from 5.2% to 0.4% on cold acquisition lists. We were able to clear our Spamhaus listing within a week and save eleven thousand dollars a month in wasted sends.”
Daniel Reyes
Head of Growth · Northwind
“Finally an email platform that doesn't treat me like a deliverability rookie. The reputation dashboards stream into our engineering Slack daily. Anyone shipping a new campaign sees the impact on inbox placement within minutes, not weeks.”
Aisha Khan
Founder · Pivot Labs
Trust & security
Built for the most regulated workloads
Security and compliance are not afterthoughts. They are the foundation that every other feature stands on.
SOC 2 Type II
Audited annually by an AICPA-accredited firm. Continuous controls monitoring. Report available under NDA on request.
GDPR + DPA
EU Standard Contractual Clauses incorporated. Pre-signed Data Processing Agreement. EU region data residency available.
TLS 1.3 + MTA-STS
Modern encryption enforced in transit at every hop. MTA-STS policy published. TLS-RPT failure reports monitored.
HIPAA-ready
Business Associate Agreement available on Enterprise. PHI-safe pipeline with audit logging and encryption-at-rest by default.
99.99% uptime SLA
Active-active multi-region architecture. Service credits issued automatically when SLA is missed. Status page driven by real probes.
SSO + SCIM
SAML 2.0 and OpenID Connect supported. SCIM provisioning for user lifecycle management. MFA enforced for staff and admin users.
Audit log exports
Tamper-evident logs of every admin action, API key event, and configuration change. Exportable to S3 or your SIEM of choice.
Bug bounty
Continuous bug bounty program. Annual third-party penetration testing. Vulnerability disclosure policy at /.well-known/security.txt.
Solutions
Built for every use case email serves
From transactional notifications to multi-million-subscriber newsletters, Inbox OSS scales with you across every email workload your business runs.
Transactional email
Receipts, password resets, security alerts, magic links — sub-second p50 delivery with idempotent retries.
Marketing email
Newsletters, product launches, broadcasts, re-engagement — built for growth teams who want to ship fast.
Notification email
System alerts, daily digests, product nudges — with frequency caps and category-aware unsubscribe.
SaaS & software
Subuser hierarchy for multi-tenant platforms, per-tenant API keys, white-label options.
E-commerce
Order lifecycle automation, abandoned-cart flows, win-back sequences, per-SKU attribution.
Fintech
SOC 2 compliance, audit log exports, regional data residency, fraud-aware routing.
FAQ
Frequently asked questions
Start sending email in under 5 minutes.
Free plan includes 3,000 emails/month forever. No credit card required.